In vehicles such as trucks or lorries, it is necessary to provide two means of braking—a service brake which is adapted to be used by the driver to control the speed of the vehicle whilst the vehicle is moving, and a parking brake which is adapted to be used by the driver to apply the brakes in a hill start situation or when the vehicle is parked. The parking brake actuator is operated to apply or release the brake by means of a manually operable control device, typically a control lever. In a conventional pneumatic braking system, in normal use, movement of the control lever causes a pneumatic signal to be sent to the parking brake actuator, and thus the position of the control lever provides a visual indication of the state of the parking brake, i.e. whether the parking brake is applied or released. Thus, it is relatively easy for a user to check that the parking brake is in the desired state, e.g. if the vehicle is to be towed that the parking brake is released.
It is becoming more common to use electrically controlled braking systems in which operation of the brake actuator is controlled by means of an electrical signal from a central controller. A manually operable control device is provided in such systems, but, typically, operation of the control lever causes an electrical demand signal to be sent to the controller, which, in turn, sends an appropriate electrical signal to a control valve to release the pneumatic pressure required to restrain the brake actuator from moving under the biasing force of a spring, thus causing the brake actuator to move under the spring force to apply the brake. In such systems it is proposed to provide the facility of automatic application of the parking brake, for example if the driver removes the keys from the ignition without applying the parking brake. Automatic operation of the parking brake would be initiated by the controller, without any movement of the control lever. Thus, it should be appreciated that, in such a system, the position of the control lever does not provide an accurate indication of the state of the parking brake.